Have found an absolutely brilliant free Keyword tool from Microsoft called Detecting Commercial Intention
Here's what the tool looks like (click image to enlarge):
All you do is type in an URL or keyword (be sure to click the buttons at the bottom to say whether you are checking a website or keyword) and then press Go. It then calculates whether it thinks it is a commercial keyword or not.
In my example, I was checking "purple carnations", because I was in the process of making a Hubpage about it. The result came back that it was a 0.93 probablity that it was commercial. So I made my hubpage - All About Purple Carnations.
However when I typed in "Nicolas Sarkozy", it came back and said that that phrase had a Non-Commercial Intention probability of 0.96. One of my very first hubs was about Sarkozy, and I can sadly confirm that this keyword tool is correct in judging commercial intention - despite loads of hits to that hub, I have only made a few cents from it. I wish I'd seen this tool earlier!
In general, I would advise people to stay away from making hubs about politics or celebrities - they may be fun to write and get loads of hits, but they don't make any money. Therefore only write such hubs for your own pleasure.